As is understood, soil is an important building material. It serves as the base for virtually all pavements, tunnels and buildings, and thus, can be thought of as an element used in construction. In construction, soil will typically be specified to have certain minimal mechanical properties, e.g., dry density, resilient modulus and strength. While some testing can be conducted in a laboratory, e.g., to determine the suitability of a raw material or blend of materials, it is also typical to perform field tests to assess the soil selection or composition, to determine appropriate site-specific compaction specifications, and to monitor for in-process quality control of the degree of compaction that affects mechanical properties of interest, typically a specified void (as reflected in density) ratio or resilient modulus.
The present field test procedures are typically density measurements made via sand cone or nuclear densitometric methods. A sand cone measurement requires substantial elapsed time while a nuclear densitometric measurement is often not considered sufficiently reliable and also raises radiation concerns. Also, mechanistic design methods require knowledge of or set specifications on soil modulus as a fundamental mechanical property of soil, not density. Accordingly, there exists a need for an ability to do rapid, low cost field tests that will reliably indicate the mechanical properties of the soil. As is understood by those skilled in the art, soil used to fill or level a construction site must be compacted, typically by the application of vibratory energy and weight, in order to obtain the requisite density and modulus. Sometimes, contractors over-compact soil as each of successive layers are added in order to ensure that the result will meet the requisite specification when completed. The ability to quickly and reliably test soil properties could significantly reduce costs due to unnecessary over-compaction and avoid longterm settlement problems due to spatially non-uniform compaction.
While it has previously been proposed to measure soil properties by dynamic impedance measurements, no such prior system has found acceptance since the readings have been found to be inconsistent and not generally repeatable.